Surge protective Device (surge protection device, SPD ) provides protection against surge current resulted from direct or indirect lightning strike or similar surge voltage. SPD is applicable to circuit with rated voltage up to 320V~, rated frequency 50/60Hz.The product, using metal oxide varistor, designed to protect both phase and neutral line, is of high electricity resistance under normal operations. In case of surge current or voltage caused by lightning strike or similar, SPD functions quickly conduct the surge voltage/current to earth and thus effectively prevent the downstream equipments of its protected line from destruction. SPD resumes its high electricity resistance to secure normal operation of the protected power network without presence of the surge voltage.